The following definitions apply to descriptions used in the specification of this invention:                UV-C—is light at the wave-length of 253.7 nm.        Seed—(in some plants referred to as a kernel) is a small embryonic plant enclosed in a covering called a seed coat with some stored food. Seed also has a general meaning that predates the above when it refers to anything that can be sown such as a seed potato that consists of a piece of a tuber.        Harvested Seed—is seed gathered from a crop when it is ripe for consumption.        Sowing Seed—is seed that is dispersed over or under the ground or other growth medium to produce a crop. Sowing seed is often treated with a coating of a pesticide to reduce root rots and insect infestation.        Hormesis—(from the Greek word hormein meaning to “excite”) describes a principle whereby a generally-favorable biological response occurs to low exposures of a stressor. A stressor eliciting hormesis thus has the opposite effect in small doses than in large doses. Something capable of exciting the favorable response is called a hormetin. In this invention the hormetin used is UV-C light.        Disinfest (disinfestation)—is the process of removal or inactivation of pests (plant pathogens and insects) from plant surfaces.        Disinfect (disinfection)—is the process of killing microorganism (fungi and bacteria) that have infected (established a food relationship) within plant tissue.        
The application of low doses of UV-C light has been used to induce a hormetic response in harvested commodities such as apple, citrus, and carrots. It has been found that low doses of UV-C light (a stressor) elicits a resistance response in a wide variety of fruits and vegetables to postharvest decay. It also delays fruit and vegetable ripening (Wilson et al. 1994, Plant Disease 78: 837-884).
Only recently has it been found that low doses of UV-C light can elicit a hormetic response in seeds that translates into a positive response in the fully developed plant. Cabbage seeds subjected to a critical low dose of UV-C light (3.6 kJ/M2) produced plants with more desirable color, greater weight, larger head diameter, and resistance to black rot disease (Brown et al. 2001, Crop Protection 20: 873-883). However, Brown et al. (2001) did not investigate the effect of irradiating cabbage sowing seed on harvested cabbage seed.
Gisenko and Mazhara (1968, Tr. Ves. Soveshch. Immuitetu. Rast. 2: 21-24) found that low doses of gamma rays, X-rays, or UV-C light irradiation applied to sowing corn seed increased disease resistance to stalk and root rots in the mature plant. Gisenko and Mazhara (1968) did not report on the effect of hormetic doses of gamma ray, X-rays, or UV-C light irradiation on yields of harvested corn kernels. Neither Brown et al. (2001) nor Gisenko and Mazhara (1968) used chemical seed pesticides (fungicides and insecticides) over-treatments in combination with a hormetic stressor on their irradiation treated seed.
Seed crop yields are dependent on a multitude of environmental factors and the genetic response of the plant to these factors. In general, conditions optimum for plant growth and development would not be expected to be optimum for seed production, which has its own set of optimum environmental and biological factors such as conditions for pollination.
The growth and reproduction of the plant is dependent on abiotic (physical) and biotic (biological) factors. Abiotic factors include the physical environmental conditions and biotic factors include animals, insects, and diseases. Each plant has certain environmental requirements for optimum growth including temperature, light, moisture, growth medium, and fertilization. Suboptimum conditions for any of these factors can result in reduced plant growth and/or reduced harvested seed yields.
Plants are also subjected to a variety of insect and disease pests for which they have varying degrees of genetic resistance. Plant breeders in developing resistance to pathogens and other pests have relied on the use of single resistance genes. Plants with the ability to resist infection by a particular pathogen are referred to as “resistant” to that pathogen. Pathogens lacking the ability to attack a particular plant are referred as “avirulent” to that plant. Unfortunately, pathogens are continually evolving strains that defeat the resistance genes deployed in crop plants by plant breeders. This has resulted in an unending “merry-go-round” of gene replacements for resistance that have been defeated by pathogens. More recently, Genetically Modified Organisms (GMO) technology is relying on the insertion of specific genes into plants for specific pest or herbicide resistance.
Synthetic pesticides are also used extensively to control plant pests. Because of concerns for safety to man and the environment, considerable opposition is being expressed to both GMOs and synthetic pesticides. This has created a demand for “greener” technologies that are less harmful to man and the environment. The present invention helps address the need for a more sustainable resistance in plants to pests. There are indications that it may provide an alternative to synthetic pesticides and consequently a reduction in the use of synthetic pesticides.
Seed treatments used to control plant diseases and insects can be divided into chemical, biological, and physical treatments. Irradiation treatments such as those described in this invention are physical seed treatments. Among the physical treatments are hot water, hot air, UV-C light, X-rays, gamma ray, and electron beam irradiation. Prior to this invention, except for the physical seed treatment investigations cited above, physical seed treatments have been used to disinfest and/or disinfect seeds from plant pathogens and insects.
It is known that certain chemicals applied to seeds will increase plant growth and enhance resistance responses in plants to pests. Hadwiger (U.S. Pat. No. 5,104,437) describes the use of the natural compound chitin applied to seeds to control root rotting organisms. Harman (U.S. Patent Publication No. 2002/0103083 A1) discloses a method of promoting deeper root development, reducing nitrogen usage in plants, and imparting drought resistance by the application of a fungus Trichoderma harzianium to plant seeds. Laby et al. (U.S. Pat. No. 7,132,525 B2) discloses fragments of an elicitor protein from Erwinia sp. that can be applied to plant seeds to elicit a hypersensitive resistance response and render plants resistant to insects. Stoner (U.S. Patent Publication No. 2008/0072494 A1) discloses a chemical elicitor combination that can be applied to seeds that contains chitosan and various micronutrients for controlling nematodes.
UV-C light and other physical stressors such as gamma ray irradiation and X-rays are known to elicit resistance responses in plants to pests. Enhanced plant pest resistance caused by elicitors of host defense such as UV-C light is thought to be caused partially by the “turn on” of Systemically Acquired Resistance (“SAR”) in the host plant (Vallad, G. E. and R. M. Goodman 2004, Crop Sci. 44: 1920-1934). Heil et al. (2001, Journal of Ecology 88: 645-654) found that when SAR was “turned on” in Triticum aestivum by an elicitor, plants developed fewer shoots and ears and thereby produced fewer seeds. It was expected that treating sowing seed of corn and soybeans with UV-C light in the present invention would result in enhanced resistance to pests, but because of the work of Heil et al. (2001) it was anticipated that the energy expended in “turning on” host resistance responses by UV-C light would result in reduced yields of harvested seed.